Ultrahigh water-absorbing fiber-forming composition

ABSTRACT

A copolymer of recurring units of at least one α,β-unsaturated monomer and recurring units of at least one copolymerizable comonomer comprising, in its preferred embodiment from about 20 to about 80 percent pendant carboxylic acid units and from about 80 to about 20 percent pendant carboxylate salt units, is blended with a heterocyclic carbonate to produce a water-absorbing composition upon curing. The composition is particularly suitable for fiber formation.

This is a divisional of co-pending application Ser. No. 834,075 filed onFeb. 26, 1986, now abandoned.

This invention relates to water-absorbing compositions.

In one of its more specific aspects, this invention relates to theincorporation of water-absorbing compositions into articles ofmanufacture for the purpose of improving the absorbent properties of thearticles.

Absorbent compositions are widely used in the manufacture of productswhich require high absorption capability. For example, water-absorbingcompositions are used in the manufacture of surgical and dental sponges,tampons, sanitary napkins and pads, bandages, disposable diapers, meattrays, and household pet litter. Water-absorbing compositions are alsoused for the modification of soil to improve water retention andincrease air capacity and for a host of other applications.

As used herein, the term "water" when used in the phrases"water-absorbing" and "water-absorbent" is understood to mean not onlywater but also electrolyte solutions such as body fluids.

A number of absorbent compositions have been developed which exhibitwater absorption capacity. For example, U.S. Pat. Nos. 3,954,721 and3,983,095 disclose preparations for derivatives of copolymers of maleicanhydride with at least one suitable vinyl monomer in fibrous form. Thefibrous copolymers are rendered hydrophilic and water-swellable byreaction with ammonia or an alkali metal hydroxide. U.S. Pat. No.3,810,468 discloses lightly cross-linked olefin-maleic anhydridecopolymers prepared as substantially linear copolymers and then reactedwith a diol or a diamine to introduce cross-linking. The resultantlightly cross-linked copolymers are treated with ammonia or an aqueousor alcohol solution of an alkali metal hydroxide. U.S. Pat. No.3,989,586 describes the preparation of sorptive paper products byincorporating cross-linked copolymers of styrene or olefins with maleicanhydride in a paper web which is then treated to convert the copolymerto a water-swellable salt form. U.S. pat. No. 3,980,663 describeswater-swellable absorbent articles made from carboxylic polyelectrolytesvia cross-linking with glycerine diglycidyl ether. U.S. pat. Nos.4,332,917 and 4,338,417 disclose blends of copolymers of styrene andmaleic anhydride with polymers derived from a monomeric ester havingvinyl unsaturation e.g., poly (vinyl acetate), cellulose triacetatecellulose aceto-butyrate, poly(ethyl-acrylate) andpoly(methyl-methacrylate). U.S. Pat. No. 4,420,588 teaches a waterabsorbing rubber composition comprising a 1,3-diene rubber and awater-absorbing resin dispersed in the rubber.

The desirability of having water-absorbing compositions in fibrous formsis well known. For example, in sanitary products such as disposablediapers and tampons, fibers can be more easily confined within theproduct. In this respect, the prior art water-absorbing compositions aredeficient; they do not facilitate fiber formation. Because of the speedof their crosslinking reactions, the prior art water-absorbingcompositions possess no appreciable shelf life; fiber formation must becompleted shortly after the compositions are prepared.

The water-absorbing compositions of this invention possess excellentshelf life. They facilitate fiber formation over a wide range of timeand temperature. They also possess excellent integrity in the hydrogelor water-swollen state, exhibit excellent water and electrolyte solutionabsorption capacity, and are readily incorporated into conventionalwater-absorbing products using conventional methods.

According to this invention there is provided a composition which iswater-absorbent upon curing comprising (a) a copolymer containing fromabout 25 to about 75 mole percent of at least one α,β-unsaturatedmonomer bearing at least one pendant unit selected from the groupconsisting of carboxylic acid units and derivatives of carboxylic acidunits and from about 75 to about 25 mole percent of at least onecopolymerizable comonomer, wherein in said copolymer from about 20 toabout 80 percent of the total pendant units introduced through theα,β-unsaturated monomer are carboxylic acid units or must be convertedinto carboxylic acid units, and from about 80 to about 20 percent of thetotal pendant units are carboxylate metal salt units or must beconverted into carboxylate salt units; and (b) a heterocylic carbonate.

According to this invention there is provided a method of producing awater-absorbing composition comprising the steps of: (a) preparing ablend of i) a copolymer containing from about 25 to about 75 molepercent recurring units of at least one α,β-unsaturated monomer whichbears at least one pendant unit selected from the group consisting ofcarboxylic acid units and derivatives of carboxylic acid units, and fromabout 75 to 25 mole percent recurring units of at least onecopolymerizable comonomer, wherein in said copolymer from about 20 toabout 80 mole percent of the total pendant units introduced through therecurring α,β-unsaturated monomer units are carboxylic acid units ormust be converted into carboxylic acid units and from about 80 to about20 percent of the total pendant units are carboxylate salt units or mustbe converted into carboxylate salt units and ii) a heterocyliccarbonate; and (b) curing the resulting blend.

According to this invention there is provided a method of absorbingwater and electrolyte solutions comprising the step of contacting thewater or electrolyte solution to be absorbed with a cured waterabsorbing composition comprising a blend of: (a) a copolymer containingfrom about 25 to about 75 mole percent of at least one α,β-unsaturatedmonomer bearing at least one pendant unit selected from the groupconsisting of carboxylic acid units and derivatives of carboxylic acidunits and from about 75 to 25 mole percent of at least onecopolymerizable comonomer, wherein in said copolymer from about 20 toabout 80 percent of the total pendant units introduced through theα,β-unsaturated monomer are carboxylic acid units or must be convertedinto carboxylic acid units, and from about 80 to about 20 percent of thetotal pendant units are carboxylate salt units or must be converted intocarboxylate salt units; and (b) a heteroxyclic carbonate.

An article of manufacture comprising a cured water-absorbing compositionand a means for supporting said composition to present said compositionfor absorption usage, wherein said water-absorbing composition comprisesa blend of: (a) a copolymer containing from about 25 to about 75 molepercent of at least α,β-unsaturated monomer bearing at least one pendantunit selected from the group consisting of carboxylic acid units andderivatives of carboxylic acid units and from about 75 to about 25 molepercent of at least one copolymerizable comonomer, wherein in saidcopolymer from about 20 to 80 percent of the total pendant unitsintroduced through the α,β-unsaturated monomer are carboxylic acid unitsor must be converted into carboxylic acid units, and from about 80 toabout 20 percent of the total pendant units are carboxylate salt unitsor must be converted into carboxylate salt units; and (b) a heterocycliccarbonate.

According to this invention there is also provided a method of enhancingat least one water absorbing characteristic of an article which methodcomprises the step of incorporating into the article a curedwater-absorbing composition comprising a blend of: (a) a copolymercontaining from about 25 to about 75 mole percent of at least oneα,β-unsaturated monomer bearing at least one pendant unit selected fromthe group consisting of carboxylic acid units and derivatives ofcarboxylic acid units and from about 75 to about 25 mole percent of atleast one copolymerizable comonomer, wherein in said copolymer fromabout 20 to about 80 percent of the total pendant units introducedthrough the α,β-unsaturated monomer are carboxyl acid units or must beconverted into carboxylic acid units, and from about 80 to about 20percent of the total pendant units are carboxylate salt units or must beconverted into carboxylate metal salt units; and (b) a heterocycliccarbonate, said composition being incorporated into the article in aneffective amount to enhance at least one water-absorbing characteristicof the article as compared to the water-absorbing characteristics of thearticle in the absence of the composition.

Copolymers suitable for use to produce water-absorbing compositions ofthe invention will contain from about 25 to about 75 total mole percentrecurring units of at least one α,β-unsaturated monomer and from about75 to about 25 total mole percent recurring units of at least onecopolymerizable comonomer. Preferably, the copolymer will contain fromabout 35 to about 65 total mole percent of recurring units of at leastone α,β-unsaturated monomer and from about 65 to about 35 total molepercent of at least one copolymerizable comonomer. Most preferably, thecopolymer will be an equimolar compolymer.

Suitable α,β-unsaturated monomers are those bearing at least one pendantcarboxylic acid unit or derivative of a carboxylic acid unit.Derivatives of carboxylic acid units include carboxylic acid saltgroups, carboxylic acid amide groups, carboxylic acid imide groups,carboxylic acid anhydride groups and carboxylic acid ester groups.

Suitable α,β-unsaturated monomers include maleic acid; crotonic acid;fumaric acid; mesaconic acid; the sodium salt of maleic acid; the sodiumsalt of 2-methyl, 2-butene dicarboxylic acid; the sodium salt ofitaconic acid; maleamic acid; maleamide; N-phenyl maleimide; maleimide;maleic anhydride; fuameric anhydride; itaconic anhydride; citraconicanhydride; mesaconic anhydride; methyl itaconic anhydride; ethyl maleicanhydride; diethylmaleate; methylmaleate; and the like, and theirmixtures.

Any suitable copolymerizable comonomer can be employed. Suitablecopolymerizable comonomers include ethylene, propylene, isobutylene, C1to C4 alkyl methacrylates, vinyl acetate, methyl vinyl ether, andstyrenic compounds having the formula: ##STR1## wherein R representshydrogen or an alkyl group having from 1 to 6 carbon atoms and whereinthe benzene ring may be substituted with low molecular weight alkyl orhydroxy groups.

Suitable C₁ to C₄ alkyl acrylates include methyl acrylate, ethylacrylate, isopropyl acrylate, n-propyl acrylate, n-butyl acrylate, andthe like, and their mixtures.

Suitable C₁ to C₄ alkyl methacrylates include methyl methacrylate, ethylmethacrylate, isopropyl methacrylate, n-propylmethymethacrylate, n-butylmethacrylate, and the like, and their mixtures.

And, suitable styrenic compounds include styrene, α-methylstyrene,p-methylstyrene, t-butyl styrene, and the like, and their mixtures.

The pendant units on the α,β-unsaturated monomer, will determine what,if any, additional reactions must be carried out to obtain a copolymerhaving the requisite pendant units necessary to produce thewater-absorbing compositions of this invention, that is, about 20 toabout 80 percent pendant carboxylic acid units and about 80 to about 20percent pendant carboxylate salt units. Preferably, both units arepresent in an amount of from about 30 to about 70 percent.

In general, if the α,β-unsaturated monomer bears only carboxylic acidamide, carboxylic acid imide, carboxylic acid anhydride, carboxylic acidester groups, or mixtures thereof, it will be necessary to convert atleast a portion of such carboxylic acid derivative groups to carboxylicacid groups by, for example, a hydrolysis reaction. If theα,β-unsaturated monomer bears only carboxylic acid salt groups,acidification to form carboxylic acid groups will be necessary.

Similarly, the final copolymer must contain from about 80 to 20 percentpendant carboxylate salt units. Accordingly, it may be necessary tocarry out a neutralization reaction. Neutralization of carboxylic acidgroups with a strong organic or inorganic base such as NaOH, KOH,ammonia, ammonia-in-water solution, or organic amines will result in theformation of carboxylate salt units, preferably carboxylate metal saltunits.

Moreover, the sequence and the number of reactions (hydrolysis,acidification, neutralization, etc.) carried out to obtain the desiredfunctionality attached to copolymer backbone are not critical. Anynumber and sequence resulting in a final copolymer which possesses fromabout 20 to about 80 percent pendant carboxylic acid units and fromabout 80 to about 20 percent pendant carboxylate salt units is suitable.

One copolymer particularly suitable for use is a copolymer of maleicanhydride and isobutylene. Another is maleic anhydride and styrene.Suitable copolymers will have peak molecular weights of from about 5,000to about 500,000 or more.

Suitable copolymers of maleic anhydride and isobutylene can be preparedusing any suitable conventional method. Such copolymers are alsocommercially available from Kuraray Isoprene Chemical Company, Ltd.,Tokyo, Japan, under the trademark ISOBAM. ISOBAM copolymers areavailable in several grades which are differentiated by viscositymolecular weight: ISOBAM-10, 160,000 to 170,000; ISOBAM-06, 80,000 to90,000; ISOBAM-04, 55,000 to 65,000; and ISOBAM-600 6,000 to 10,000.

To produce a water-absorbing composition of this invention, at least onecopolymer and at least one heterocyclic carbonate are blended such thatthe water-absorbing composition contains in weight percent, from about80 to about 99.5 total copolymer and from about 0.5 to about 20heteracyclic carbonate. Preferably, the composition will contain fromabout 90 to about 99 weight percent total copolymer and from about 1 toabout 10 weight percent total heterocyotic carbonate.

Any suitable heterocyclic carbonate can be employed Preferably theheterocyclic carbonates are those represented by the following generalstructure: ##STR2## wherein each R separately represent a hydrogen atom,an alkyl group, an aromatic group, a halogen group, a substitute alkylgroup, or a substituted aromatic group.

Heterocyclic carbonates represented by the above structure includepropylene carbonate, ethylene carbonate, 1,2-butylene carbonate,2,3-butylene carbonate, phenylethylene carbonate and the like, and theirmixtures. Propylene carbonate is preferred.

The water-absorbing composition of this invention can be prepared usingany suitable blending method such as described in the Examples whichfollow. After the water-absorbing composition is prepared, but typicallybefore it is cured and in some instances as it is curing it is processedinto any desired form using conventional methods of fabrication. Forexample, the water-absorbing composition can be subjected to casting;spray drying; air-assisted spray drying; air attenuation; wet, dry orflash spinning; and the like. The selection of the process is typicallydictated by the shape or form needed for end use. Forms that thewater-absorbing composition may be fabricated into include films orsheets, powders and granules, fibers and any form into which fibers canbe processed such as for example milled fibers, chopped fibers, fluff orbulk fibers, strands, yarns, woven fabrics, nonwoven mats and the likeusing a variety of methods, including twisting, beaming, slashing,warping, quilling, severing, texturizing, weaving, knitting, braidingetc.

While not meaning to be limited to any theory, the heterocycliccarbonate is believed to serve as a high temperature, slow-reacting,cross-linking agent for the copolymer resulting in the formation ofcovalent cross-link bonds upon curing. For example, it has been foundthat, if a styrene-maleic anhydride copolymer is blended with propylenecarbonate to form a water-absorbing composition according to thisinvention, a temperature about 150° C. or higher is typically requiredto cure. Similarly, if an ethylene-maleic anhydride copolymer isemployed, a temperature of 140° C. or higher is typically needed tocure. And, if an isobutylene-maleic anhydride copolymer is employed, atemperature of 200° C. or higher is typically needed to cure.

Without meaning to limit the invention, the water-absorbing compositionsof this invention are particularly well suited for being made intofibers because of the wide time and temperature ranges in which they canbe shaped. More specifically, the water-absorbing compositions of thisinvention can be formulated to cure at temperatures within the range offrom about 140° C to about 250° C. or higher and possess shelf lifes inexcess of two months as demonstrated in Example 11. Hence, thewater-absorbing compositions of this invention can be easily made intofibers using conventional methods and equipment.

The water-absorbing compositions of this invention and articles ofmanufacture into which the compositions are incorporated are suitablefor use in a wide range of absorptive functions. In general, thearticles into which the water-absorbing compositions are incorporatedserve the function of supporting the composition and presenting it in aform adapted for absorptive end use. Means to support and present thecomposition for absorptive use include, but are not meant to be limitedto bandages, surgical and dental sponges, tampons, sanitary napkins andpads, disposable diapers, meat trays, pads for absorption ofperspiration, and the like.

In one embodiment, a water-absorbing composition of this invention isincorporated into a disposable diaper, using conventional fabricationmethods to form a diaper composite having the following typical layers:(1) an outer (away from the body) of impermeable polyethylene film; (2)a first cellulosic pulp layer superimposed on the film; (3) a layer of acured water-absorbing composition of this invention in the form of e.g.powder, fibers, flugg e.g. a fibrous mass, a non-woven fiber mat or awoven fabric; (4) an optional, second cellulosic pulp layer and (5) aninner permeable polyethylene film layer.

Fibers made from the water-absorbing compositions of this invention areparticularly suitable for absorbent applications. It is well known thata mass of fibers provides a large surface area for contact with theliquid material to be absorbed and because fibers can be easily confinedwithin the article into which they are incorporated.

The following examples serve to further demonstrate the invention.

EXAMPLE I

This example demonstrates the preparation of a copolymer of anα,β-unsaturated monomer and a copolymerizable comonomer suitable for usein the practice of this invention.

A solution of about 240 g of maleic anhydride, about 255 g of styrene,and 2370 ml of methyl ethyl ketone was prepared and introduced into aone gallon stirred reactor at room temperature under a nitrogenatmosphere. Free radical polymerization was initiated by charging about8.20 g of VAZO 65 polymerization initiator (azoisobutyronitrile E. I.DuPont) into the reactor. The polymerization reaction was conducted forabout 24 hours at a temperature of about 55° C. Net, tetrahydrofuran wasadded to dilute the reactor contents. And the polymerization product, acopolymer of styrene and maleic anhydride, was recovered byprecipitation into methanol with high speed stirring. The copolymer wasdried overnight at 30° C in a vacuum oven, and then at 90° C for aboutone hour. About 499 g of copolymer were recovered.

The dried styrene-maleic anhydride copolymer was analyzed by titrationof maleic acid and found to contain 43 mole percent maleic anhydride(41.7 wt.%). The balance of the copolymer was styrene. The copolymer wasfound to have a glass transition temperature of 234° C by differentialscanning calorimetry and a peak molecular weight of 108,000 by gelpermeation chromatography using polystyrene standards.

EXAMPLE 2

This example demonstrates the preparation of five water-absorbingcompositions of the invention using the styrene-maleic anhydridecopolymer of Example 1. A series of five water-absorbing compositions (Ithrough V) was prepared. Each composition was individually prepared asfollows.

About 10 g of the copolymer and about 150 g of demineralized water wereadded to a mixing vessel with agitation and the vessel contents wereheated to about 90° C. At a temperature of about 90° C a solution of apredetermined amount of sodium hydroxide (98.9% purity, pellets) in 10 gof dimineralized water was slowly added to the mixing vessel over a onehour period with agitation. The amount of sodium hydroxide added to eachcomposition was calculated to convert, here, neutralize, a certainpercentage of the pendant carboxylic acid units (which were convertedfrom acid anhydride units) into carboxylate sodium salt units. After theaddition was completed, agitation was continued for about one hour andthe copolymer dissolved into the solution.

The resulting copolymer-containing solution was cooled to roomtemperature and 0.5 g of propylene carbonate (99% purity, AldrichChemical) was added to the solution with agitation. The resultingcomposition was poured onto Mylar film.

The composition on the Mylar film was allowed to air dry and thenfurther dried in a vacuum oven for 30 minutes at 60° C. The compositionwas ground into particles having diameters of about 300 microns andcured at 160° C. for about 30 minutes in a hot air circulation oven.

Using the above-described procedure, five water-absorbing compositions(I-V) were prepared, employing the amounts of sodium hydroxide set forthin following table. Moreover, each composition, was subjected to testingto determine its Swell Index, Percent Solubility, and the results arealso shown in the Table. The test procedures used to determine SwellIndex and Percent Solubility are described below.

    ______________________________________                                        Composition     I      II     III  IV   V                                     ______________________________________                                        Amount of NaOH added (g)                                                                      1.27   1.7    1.98 2.13 3.4                                   % Pendant carboxylate                                                                         37     50     58   63   100                                   Metal Salt Units                                                              Swell Index                                                                   @ Atm. Pressure 17.8   41.9   53.8 49.7 Soluble                               @ 0.5 psi       13.4   29.6   41.8 39.3 Soluble                               ______________________________________                                    

Swell Index

This test procedure is described in U.S. Pat. No. 4,454,055 theteachings of which are incorporated herein by reference thereto. Thetest procedure and equipment used herein were modified slightly ascompared to the procedure and equipment described in U.S. Pat. No.4,454,055.

To determine the Swell Index at atmospheric (room) pressure, about 0.2to 0.3 g of the water-absorbing composition to be tested is placed in anempty W-shaped tea bag. The tea bag containing the composition isimmersed in brine (0.9 wt.% NaCl) for 10 minutes, removed and allowed osit on a paper towel for 30 seconds to remove surface brine. The SwellIndex of the composition, that is, the units of liquid absorbed per eachunit of sample is calculated using the following formula: ##EQU1##

To determine Swell Index under pressure, the following modifiedprocedure was used.

After the tea bag containing the sample composition is immersed in brineand surface brine is removed, it is immediately placed in a 16 cm IDBuchner funnel fitted with a 2000 ml sidearm vacuum filter flask andconnected to a manometer. Then, a piece of dental dam rubber sheeting issecurely fixed over the mouth of the funnel such that the sheeting justrests on the tea bag. Next, a vacuum sufficient to create the desiredpressure is drawn on the flask for a period of five minutes, and, theSwell Index under pressure is calculated using the above formula.

Percent Solubility

About 0.5 g of the water-absorbing composition sample to be tested isdispersed in about 150 g of brine (0.9 wt.% NaCl) at room temperaturefor 20 minutes with occasional gentle agitation. After 20 minutes, themixture is filtered through a 150 micron polypropylene screen. Next, thefiltrate is dried to a constant weight in an oven and the weight ofsoluble composition determined by subtracting the weight of the NaClfrom the total weight of the dry filtrate. Percent solubility is thendetermined using the following formula: ##EQU2##

EXAMPLE 3

This example demonstrates the preparation of a water-absorbingcomposition of this invention using substantially the procedure ofExample 2 and further illustrates the effect of different curetemperatures on its absorbent properties.

Using substantially the procedure described in Example 2, about 10 g ofthe styrene-maleic anhydride copolymer produced in Example 1 werehydrolyzed and then partially neutralized with 1.7 g, of sodiumhydroxide to convert about 50% of the pendant carboxylic acid units onthe copolymer to carboyxlate sodium salt units. Next, the resultingcomposition (VI) was blended with 10 phr (9.1 wt.%) of propylenecarbonate and, the composition was divided into thirds. Each third wascured for thirty minutes at a different cure temperature. One was curedat 150° C; one at 160° C. and the other at 170° C. The results were asfollows:

    ______________________________________                                        Composition  VI          VI      VI                                           ______________________________________                                        Cure Temp. (°C.)                                                                    150         160     170                                          Swell Index                                                                   @ Atm. Pressure                                                                            37.5        23.1    16.5                                         @ 0.5 psi    28          16.9    12.7                                         % Solubility 12.8        8.3     6.4                                          ______________________________________                                    

EXAMPLE 4

This example demonstrates the preparation of two water-absorbingcompositions of the invention using substantially the procedure ofExample 2, as herein described. Data illustrative of the effect ofheterocyclic carbonate content on absorbent properties are alsopresented below.

Using substantially the procedure of Example 2, Composition II, threecompositions (VII and VIII, and a Control) were prepared. Allcompositions were hydrolyzed and partially neutralized with NaOH toconvert about 50% of the pendant carboxylic acid units to carboxylatesodium salt units.

Composition VII differed from Composition II in that it was prepared byblending the styrene-maleic anhydride copolymer with 10 phr of propylenecarbonate.

Composition VIII differed in that it was prepared by blending thecopolymer with 15 phr of propylene carbonate

No propylene carbonate was added to the Control composition.

The results of the effect of propylene carbonate content on absorbentproperties of these compositions are set forth below. The absorbentproperties of Composition II are listed for comparative purposes; itemployed 5 phr of propylene carbonate.

    ______________________________________                                        Composition    Control    II     VII    VIII                                  ______________________________________                                        Propylene Carbonate (phr)                                                                    0          5      10     15                                    Swell Index:                                                                  @ Atm. Pressure                                                                              Soluble    41.9   23.1   24.4                                  @ 0.5 psi      Soluble    29.6   16.9   16.8                                  % Solubility   100        12.8   8.3    9.8                                   ______________________________________                                    

EXAMPLE 5

This example demonstrates the preparation of a water-absorbingcomposition of this invention using an equimolar, alternating copolymerof ethylene-maleic anhydride designated EMA-31 (100,000 molecular wt.),commercially available from Monsanto.

About 15 g of EMA-31 copolymer, 150 g of demineralized water and 0.6 g(4 phr) of propylene carbonate were added to a mixing vessel withagitation and heated to about 90° C. When the contents of the vesselreached about 90° C., about 4.85 g of NaOH dissolved in 20 ml water wereslowly introduced over a 30 minute period.

After the NaOH addition was completed, the contents of the mixing vesselwere agitated for about 30 minutes after which the EMA-31 copolymer wasobserved to be completely dissolved. The pH of the resulting solutionwas about 6.

Water in the resulting solution was allowed to evaporate until a solidcomposition was obtained and the solid composition was further dried ina vacuum oven at 50° C for 2 hours. Next, the composition was groundinto a powder having particle diameters of about 300 microns and thepowder was cured at 160° C for 30 minutes in a hot air circulation oven.

The absorbent properties of the resulting water-absorbing. CompositionIX, are shown in the following table.

    ______________________________________                                        Composition            IX                                                     ______________________________________                                        % Pendant Carboxylate Salt Units                                                                     50                                                     Swell Index:                                                                  @ Atm. Pressure        25.7                                                   @ 0.1 psi              22.7                                                   @ 0.5 psi              18.3                                                   @ 1.5 psi              16.9                                                   % Solubility           9.6                                                    ______________________________________                                    

EXAMPLE 6

This example demonstrates the preparation of two water-absorbingcompositions of this invention (Compositions X and XI) usingsubstantially the procedure of Example 5, as herein described.

Composition X differed from the procedure and materials of Example 5 inthat the EMA-31 copolymer was blended with one phr of ethylenecarbonate.

Composition XI differed from the procedure and materials of Example 5 inthat the EMA-31 copolymer was blended with one phr of ethylene carbonateand cured at 150° C.

The absorbent properties of Compositions X and XI were as follows:

    ______________________________________                                        Composition         X       XI                                                ______________________________________                                        Ethylene Carbonate (phr)                                                                          1       1                                                 Cure Temperature (°C.)                                                                     160     150                                               Swell Index:                                                                  @ Atm. Pressure     31.3    37.6                                              @ 0.1 psi           30.4    34.3                                              @ 0.5 psi           26.1    28.7                                              @ 1.5 psi           21.9    24.6                                              % Solubility        14.2    15.1                                              ______________________________________                                    

EXAMPLE 7

This example demonstrates the preparation of a water-absorbingcomposition of this invention, Composition XII, using ISOBAM 10, anisobutylene/maleic anhydride copolymer commercial available from KurarayIsoprene Chemical Company, Ltd. ISOBAM 10, has a molecular weight of170,000, and a maleic anhydride content of about 59.3 wt.% (46.6 mole %)as determined by titration of maleic acid.

About 957 g of the isobutylene-maleic anhydride copolymer, and about1740 g of demineralized water were charged to a one gallon stirredreactor and heated to about 90° C. A solution of 248 g of NaOH dissolvedin about 372 g of water was added slowly to the reactor over a 45 minuteperiod. Next, 47.8 g (5 phr) of propylene carbonate were introduced intothe reactor and the reactor contents were stirred for about 10 hour todissolve the isobutylene-maleic anhydride copolymer. The pH of theresulting solution was 6.5. The neutralization reaction resulted inabout 53.5% of the pendant units on the 46.6 mole % recurring units ofmaleic anhydride being converted carboxylate sodium salt units.

The resulting solution was allowed to cool to room temperature and thenatenuated into fibers by forcing the solution through an orifice into acurrent of warm air and wrapping the resulting attenuated fibers onto aMylar film covered drum. The resulting fibers had diameters of about 10microns. Two fibrous mass samples of the fibers produced from theresulting Composition XII were separately cured for 30 minutes at 210°C. and at 220° C.

The following table illustrates the absorbent properties of CompositionXII in fiber form.

    ______________________________________                                        Composition (fibers)                                                                              XII     XII                                               ______________________________________                                        Cure Temperature (°C.)                                                                     210     220                                               Swell Index:                                                                  @ Atm. Pressure     36.3    33.4                                              @ 0.5 psi           26.0    21.8                                              % Solubility        17.7    15.5                                              ______________________________________                                    

EXAMPLE 8

This example demonstrates the preparation of four water-absorbingcompositions of this invention (Compositions XIII-XVI) usingsubstantially the materials and procedure of Example 7.

Each composition was prepared using an isobutylenemaleic anhydridecopolymer (ISOBAM 10) which had been treated to covert 53.5% of thependant units, introduced into the copolymer through the 46.6 mole %recurring units of maleic anhydride, to carboxylate salt units.

All four compositions were ground into power and the powers wereseparately cured and their absorbent properties tested.

The absorbent property data obtained for the four compositions preparedin accordance with the listed composition and procedure data are shownin the following table.

    ______________________________________                                        Composition    XIII    XIV     XV    XVI                                      ______________________________________                                        Propylene Carbonate (phr)                                                                    0       0       0     1                                        Ethylene Carbonate (phr)                                                                     1       2       5     1                                        Cure Temperature (°C.)                                                                210     210     210   210                                      Cure Time (min)                                                                              30      30      30    30                                       Swell Index                                                                   @ Atm. Pressure                                                                              66.5    51.8    31.4  58.5                                     @ 0.1 psi      59.7    43.6    31.1. 58.6                                     @ 0.5 psi      53.0    39.5    24.3  50.0                                     @ 1.5 psi      48.0    37.8    22.1  47.5                                     % Solubility   19.8    12.3    11.3  16.5                                     ______________________________________                                    

EXAMPLE 9

This example demonstrates that the water-absorbing compositions of thisinvention possess excellent integrity in the hydrogel state.

A sample of Composition II, (taken before curing) was cured at 180° Cfor 30 minutes. Next, a 2.2885 g. sample of the cured composition wassubjected to Soxhlet extraction using 500 ml of distilled water. Theextraction was run at refluxing temperature for about 6 hours. Theextracted polymer gel was recovered by drying in a vacuum oven at 100° Cfor 20 hours. The extracted, dried composition weighed 2.1147g.

The amount of soluble product found was 0.1738 g or 7.6 wt. %. Nopropylene carbonate residue was found in the extracted solution.

The results of Swell Index testing done on the extracted compositionwere as follows:

    ______________________________________                                                    Extracted Composition                                             ______________________________________                                        Swell Index:                                                                  @ Atm. Pressure                                                                             37.4                                                            @ 0.1 psi     33.6                                                            @ 0.5 psi     23.6                                                            @ 1.5 psi     26.2                                                            ______________________________________                                    

The above data indicate that the water-absorbing compositions of thisinvention possesses excellent absorbent properties after Soxhletextraction. Moreover, the test results indicate that the water-absorbingcompositions are crosslinked through covalent bonds.

EXAMPLE 10

This example demonstrates the preparation of fibers of differentdiameters from the water-absorbing composition of Example 7--Composition XII.

Fibers of four different diameters 6, 75, 110, and 190 microns, wereprepared by air attenuation of a liquid stream of Composition XII(before curing) using a spray nozzle assembly of the type commerciallyavailable from Spraying Systems Company, Wheaton, Ill., modified to beconical at the tip to reduce turbulent air flow.

After the fibers having different diameters were formed, they wereseparately cured at 210° C for 30 minutes and then the fibers weretested for absorbency. The test results are shown below.

    ______________________________________                                        Composition    XII      XII    XII     XII                                    ______________________________________                                        Fiber diameter (microns)                                                                     6        75     110     190                                    Swell Index:                                                                  @ Atmospheric Pressure                                                                       34.1     52.4   69.5    65.2                                   @ 0.5 psi      28.0     36.6   51.8    56.8                                   % Solubility   18.1     12.4   14.7    11.8                                   ______________________________________                                    

The above data illustrate that fibers produced from a water-absorbingcomposition of this invention have been found to be capable of absorbingup to 69.5 times their weight.

EXAMPLE 11

This example demonstrates that the water-absorbing compositions of thisinvention possess excellent shelf life when in solution form.

Two samples of the solution used to produce Composition XII were aged.One sample was aged for one month at ambient temperature and then for 2days at 100° C. The other sample was aged for two months at ambienttemperature. After aging, fibers were prepared from the solutions andthe resulting fibers were cured for 30 minutes at 210° C.

The absorbent property data of the fibers produced after aging arecompared with the absorbent property data of the fibers produced inExample 7, in the absence of aging.

    ______________________________________                                        Composition     XII       XII     XII                                         ______________________________________                                        Time of Solution Aging                                                                        0         1 mo.   2 mo.                                       Swell Index:                                                                  @ Atmospheric Pressure                                                                        36.3      37.2    38.0                                        @ 0.1 psi       30.0      30.8    29.9                                        @ 0.5 psi       26.0      26.6    24.9                                        @ 1.5 psi       23.6      24.1    21.2                                        % Solubility    17.7      16.4    18.6                                        ______________________________________                                    

The above data illustrate that, even after aging a water-absorbingcomposition of this invention for two months and then forming fibers,the fibers showed no appreciable change in their Swell Index values,hence indicating no appreciable loss in absorption properties.

It will be evident from the foregoing that various modifications can bemade to this invention. Such, however, are considered as being withinthe scope of the invention.

What is claimed is:
 1. A stable, heat curable, aqueous compositioncomprising in weight percent:(a) from about 80 to about 99.5 of acopolymer containing from about 25 to about 75 mole percent of about 20to about 80 percent neutralized carboxylic acid substituted ethylenicunits and from about 75 to about 25 mole percent recurring units of atleast one copolymerizable comonomer; and (b) at least one heterocycliccarbonate compound wherein the resulting aqueous composition is uncuredand stable at room temperature.
 2. A method of rendering the aqueouscomposition of claim 1 water-absorbing which comprises heating thecomposition to a temperature sufficient to cure.
 3. A method ofabsorbing water and electrolyte solutions which comprises contacting thewater of electrolyte solution to be absorbed wit the cured compositionof claim
 1. 4. A method of producing a water-absorbing compositioncomprising the steps of:(a) preparing a blend of (i) from about 80 toabout 99.5 of a copolymer containing from about 25 to about 75 molepercent recurring units of at least one α,β-unsaturated monomer bearingat least one pendant unit selected from the group consisting ofcarboxylic acid units and derivatives of carboxylic acid units and fromabout 75 to about 25 mole percent recurring units of at least onecopolymerizable comonomer, wherein in said copolymer from about 20 toabout 80 percent of the total pendant units introduced through therecurring units of the α,β-unsaturated monomer must either be carboxylicacid units or must be converted into carboxylic acid units and fromabout 80 to about 20 percent of the total pendant units must either becarboxylate salt units or must be converted into carboxylate metal saltunits; and (ii) from about 0.5 to about 20 weight percent of aheterocyclic carbonate; and (b) curing the resulting blend.
 5. Themethod of claim 4 comprising the step of forming the blend into a shapedarticle the blend is prepared but before it is fully cured.
 6. Themethod of claim 5 in which the blend is formed into fibers.
 7. Themethod of claim 5 in which the blend is formed into a powder.
 8. Themethod of claim 5 in which the blend is formed into a film.
 9. Themethod of claim 4 in which said curing is induced by heating the blend.10. A stable, heat curable, aqueous composition which is water-absorbentupon curing comprising in weight percent:(a) from about 80 to about 99.5of a copolymer containing from about 25 to about 75 mole percentrecurring units of at least one α,β-unsaturated monomer bearing at leastone pendant unit selected from the group consisting of carboxylic acidunits and derivatives of carboxylic acid units and from about 75 toabout 25 mole percent mole percent recurring units of at least onecopolymerizable comonomer, wherein in said copolymer from about 20 toabout 80 percent of the total pendant units introduced through therecurring units of the α,β-unsaturated monomer must either be carboxylicacid units or must be converted into carboxylic acid units, and fromabout 80 to about 20 percent of the total pendant units must either becarboxylic salt units or must be converted into carboxylate salt units;and (b) from about 0.5 to about 20 of a heterocyclic carbonate, whereinthe resulting aqueous composition is uncured and stable at roomtemperature.
 11. The composition of claim 10 in which said copolymercontains from about 35 to about 65 mole percent recurring units of saidat least one α,β-unsaturated monomer and from about 65 to about 35 molepercent of said at least one copolymerizable comonomer.
 12. Thecomposition of claim 10 in which said copolymer is an equimolarcopolymer.
 13. The composition of claim 10 comprising in weight percentfrom about 90 to about 99 of said copolymer and from about 1 to about 10of said heterocyclic carbonate.
 14. The composition of claim 10 in whichsaid copolymer is a copolymer of styrene and maleic anhydride.
 15. Thecomposition of claim 10 in which said copolymer is a copolymer ofethylene and maleic anhydride.
 16. The composition of claim 10 in whichsaid copolymer is a copolymer of isobutylene and maleic anhydride. 17.The composition of claim 10 in which said heterocyclic carbonate ispropylene carbonate.
 18. The composition of claim 10 in which saidheterocyclic carbonate is ethylene carbonate.
 19. A method of absorbingwater and electrolyte solutions which comprises contacting the water orelectrolyte solution to be absorbed with the cured composition of claim10.
 20. The aqueous composition of claim 10 in being heat curable at atemperature of about 140° C. or higher.